1. Field of the Invention
The present invention relates to a furnace of a boiler for a power plant, in which a combustion space defined between an outer water tube section and an inner water tube section is formed in a shape closest to the natural shape of a flame so that the contact area between the water tube sections and the flame is increased to increasing the temperature of water heated in the water tube sections of the furnace, thereby enhancing the thermal efficiency.
Also, the present invention relates to a furnace of a boiler for a power plant, in which water fed to the furnace is again fed to an inner water tube section via an outer water tube section so that a load of a feed water pump is greatly reduced, thereby increasing the thermal efficiency of the entire system, and an inner water tube wall prevents formation of a fire ball and act as a superheater so as to absorb heat generated from flames in a large amount, thereby preventing the thermal NOx formation caused by a high-temperature fire ball and preventing an ash combustion residue from being molten by the high-temperature fire ball to form slag.
In addition, the present invention relates to a furnace of a boiler for a power plant, in which water fed to the furnace is primarily heated to be separated into hot water and steam in an outer water tube section, and only the separated steam is secondarily heated in an inner water tube section so as to produce a superheated steam more rapidly than in the case where water and steam are heated.
2. Background Art
In general, a boiler widely used in a thermoelectric power plant is largely divided into a coal fired boiler, an oil fired boiler and a gas fired boiler. Among them, the coal fired boiler occupies the majority of the amount of electricity generation, and is roughly classified into a pulverized coal-fired boiler and a fluidized bed boiler.
Since the pulverized coal-fired boiler burns a pulverized (or powdered) coal, it shows a high combustion efficiency but produces nitrogen oxides (NOx) harmful to the atmospheric environment due to high-temperature combustion. Thus, the pulverized coal-fired boiler is adopted in a large-scale power plant which is equipped with a large-sized dust collector capable of treating the nitrogen oxides (NOx). Since the fluidized bed boiler burns coarse coal particles, it is inhibits production of the nitrogen oxides (NOx) due to the low combustion temperature. Thus, in order to improve the heat transfer effect in which the heat of the flame is transferred to water tubes, the fluidized bed boiler heats allows sand granules to be blown upwardly from the bottom of the furnace to heat the sand granules and allows the thus heated sand granules to be moved downwardly along a water tube section disposed at the outside of the furnace, thereby improving the thermal efficiency.
For this reason, in case of the pulverized coal-fired boiler having a high combustion efficiency, the researches are actively in progress to inhibit production of the nitrogen oxides (NOx). Meanwhile, in case of the fluidized bed boiler, attempts are being made to expand the scale of the furnace to improve the thermal efficiency.
In the present invention, an example of the pulverized coal-fired boiler occupying the majority of the coal burning thermal power generation will be described.
A conventional pulverized coal-fired boiler is constructed such that a water tube measuring 7 kilometers in length is arranged in a zigzag pattern in the vertical and horizontal directions so as to maximally absorb the heat from flame erupting upwardly.
Since such a conventional pulverized coal-fired boiler adopts a method in which a plurality of water tubes are densely arranged vertically to increase the heat absorption efficiency from the flame, a load of a feed water pump is abnormally increased which circulates water while forcibly reversing the natural flow direction of the steam so that the water flows an elongated small-diameter water tube having a large flow resistance.
A motor driving this feed water pump consumes 30-40% of the power plant internal consumption. Also, the conventional pulverized coal-fired boiler entails a disadvantage in that it exhausts the nitrogen oxides (NOx) in a large amount, melts the ash to form sticky slag to thereby produce a large amount of clinker, and fouls the filter, which makes impossible to use an inexpensive low-rank coal.
In order to solve such a problem, as shown in FIG. 1, there is proposed a construction of a furnace of a pulverized coal-fired boiler of Korean Registration Patent No. 10-0764903, in which an inner water tube wall 8 consisting of a plurality of water tubes is installed vertically at the center of an outer water tube wall 6 disposed vertically adjacent to the inner circumference of the furnace so that the fuel injected from fuel injection nozzles mounted on the outer water tube wall 6 is burnt while rotating along the outer circumference of the inner water tube wall 8 to create a tubular pillar of fire between the inner and outer water tube walls 8 and 6, thereby preventing a phenomenon in which the flame is concentrated in one spot to be raised to an ultra-high temperature as well as so that air lower in temperature than the flame is introduced into a combustion space S defined between the inner and outer water tube walls 8 and 6 through air injection holes formed in the inner water tube wall 8 so as to prevent the flame (F) from being excessively raised to an ultra-high temperature, thereby reducing the amount of nitrogen oxides (NOx) generated upon the burning of nitrogen in the air by the high-temperature flame. However, the Korean Registration Patent No. 10-0764903 still involves a problem in that a lot of heat of the convective gas generated in the furnace is not transferred to and absorbed by a water tube section of the furnace, but is moved upwardly to absorb the remained heat while passing through a superheater and a reheater, resulting in a great increase in the height of an upper layer of the furnace.